1. Field of Invention
The present invention relates, in general, to a transmission clutch and, more particularly, to a torque estimation method for a transmission clutch which estimates an accurate torque value that is transmitted via slip in the clutch, in particular, a dry clutch of a dual clutch transmission (DCT).
2. Description of Related Art
Recently, many developments have been made in dual clutch transmissions (DCTs) which can realize the convenience of driving of an automatic transmission and the fuel efficiency and high power efficiency of a manual transmission. A DCT refers to an automated transmission based on a manual transmission, and is a system that has two torque transmission shafts and automatically controls a clutch without a torque converter. The DCT has the advantage of high fuel efficiency. However, since the DCT system using a dry clutch causes the clutch to directly engage two working parts without the torque converter, the ability to control the clutch determines the performance of departure and gear-shifting of a vehicle. In addition, since it is impossible to directly measure a transmission torque occurring at the frictional surfaces of clutch disks, it is important to determine the clutch transmission torque using information on a preset value of a sensor mounted in the vehicle.
A conventional clutch torque estimation method uses the observer theory of control engineering. This is a method of calculating a transmission torque that occurs when a clutch disk slips based on an engine torque. Here, the engine torque output from an electronic control unit (ECU) is based on data produced through repeated tests in the static state. However, since the point of time where clutch torque information is required always corresponds to the transient state (creep, departure, or the like) of the engine, a difference occurs between the engine torque of the ECU and an actual value. Therefore, the clutch torque estimation value produced based on the unreliable engine torque also has an error, which is problematic.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.